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Cotton Report 1993

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The
Cotton Report is one of several commodity-based agricultural
research reports published by the University of Arizona.

This report, along with the
Forage and Grain Report, was established by Hank Brubaker,
Extension Agronomist, after seeing a similar report published by
Texas A&M University in the mid-1970’s.

The purpose of the report is to provide an annual research
update to farmers, researchers, and those in the agricultural
industry. The research is conducted by University of Arizona and
USDA-ARS scientists.

Both historical and current
Cotton Reports have been made available in the UA Campus
Repository as part of a collaboration between the College of
Agriculture and Life Sciences and the University Libraries.

Recent Submissions

Field experiments were conducted at three locations in Arizona (Maricopa, Marana, Safford) to evaluate 9 cottonseed treatments on Upland cotton (G. hirsutum L.). Stand counts were taken to evaluate the effectiveness of each treatment. Statistical analysis showed no significant differences among the treatments used at the Maricopa location. Significant differences were found among the treatments used at the Marana and Safford locations.

The germination percentage and seedling respiration were evaluated on 11 cultivars of Cotton produced in Arizona. Respiration rates of 5-day old seedlings ranged from 6.0 to 16.9 mg /g⁻¹ hr⁻¹ for DP -5690 and KC-311, respectively. Germination percentage ranged from 31 to 87% for KC-311 and DP-51, respectively. A significant negative correlation (r = -.90) between respiration rates and the germination percentage indicates that seed quality is closely associated with early seedling metabolic rates.

In a mail survey, we asked Arizona cotton growers which characteristics of a tillage system are important to them. Burial of crop residue, low cost, easy maintenance, reliability, low field work time, and breaking insect life cycles were all rated as important characteristics. Dust control was rated as not important. In rating their perceptions of conventional and alternative tillage systems, cotton farmers indicated that they were not completely satisfied with any of the currently available tillage alternatives.

Two reduced cotton tillage systems, both of which utilize controlled traffic farming techniques, are being compared to a conventional tillage system in terms of energy requirements, field work time requirements, crop yield, and operating costs. Four seasons of testing show the Sundance system to have the lowest energy requirement of 28.2 HpHr /Ac, the Uprooter-Shredder-Mulcher (USM) the second lowest at 40.5 HpHr /Ac, and conventional tillage the highest at 54.4 HpHr /Ac. Field work times of the two reduced tillage systems are about one-half that of conventional tillage. Costs of the two reduced tillage systems are lower than for conventional tillage. We have never measured a significantly lower lint yield with either of the two reduced tillage systems, relative to conventional tillage.

With controlled traffic tillage, the field is divided into "traffic zones" to which all wheel traffic is confined and `production zones" where the plants are grown and there is no wheel compaction. Researchers have shown that using this concept can result in significantly lower tillage costs and field work time than with conventional "broadcast" tillage systems. Most researchers have shown that controlled traffic cotton yields are as high, and are sometimes higher than with conventional tillage. In our research, we have not measured any differences in yield or soil compaction between controlled traffic and conventional tillage systems.

A replicated field study was conducted at the Maricopa Agricultural Center in 1992 investigating Upland cotton lint yield and fiber quality response to foliar applied potassium thiosulfate. Applications were applied at early, peak, and late bloom. There were no significant yield or lint quality response by treatment.

Due to a limited information describing the response of cotton (Gossvpium spp.) in Arizona to K fertilization, three studies were conducted in 1992 with the objective of evaluating the response of cotton crop growth and lint yield to soil and/or foliar applications of K fertilizer. The locations of the trials included the Safford Agriculture Center (Pima clay loam), Maricopa Agriculture Center (Casa Grande sandy loam), and a site located near Coolidge, AZ on a Mohall sandy loam soil. All irrigation, pest management, and fertilization inputs (other than K) were provided on an as- needed basis throughout the season. Routine plant measurements and plant mapping analyses were carried out at each location on regular intervals throughout the season. At the Safford location both Upland (G. hirsutum L., var DPL 90) and Pima (G. barbadense L., var S-6) cotton were planted with treatments including soil and foliar K applications imposed in a factorial arrangement. All soil K applications were broadcast and preplant incorporated using K₂SO₄ as the K source at rates of 0, 200, and 400 lbs. K₂O/acre. Four 4.6 lbs K₂O /acre foliar applications of KNO₃ were applied at 1626, 2016, 2326, and 2510 heat units after planting (HUAP). The trial at the Maricopa Agriculture Center included four foliar K applications over the growing season applied to Pima cotton (S-6) at 2427, 2762, 3200, and 3515 HUAP. The six foliar treatments included rates which ranged from 0 to 37 lbs. K₂O /acre using KNO₃ as the K source. Treatments were arranged over the experimental area in a randomized complete block design with five replications. At Coolidge all K treatments were band-applied to the soil at a depth of 8 in. using two shanks per row, preplant. The treatments were 0, 218, 436, and 654 lbs. K₂O /acre using K₂SO₄ as the fertilizer source. Upland cotton (STV KC311) was planted and treatments were arranged in a randomized complete block design with four replications. Results from all three trials indicated no differences among any of the treatments (including soil verses foliar and unfertilized treatments). All of the plant measurements taken for all the locations reveal crop growth resulting in excellent fruit retention without vegetative growth (i.e. height-to-node ratios within the long -term 95% confidence intervals for both Upland and Pima cotton. This indicates ample nutrient demand so that if available soil K is inadequate to meet crop needs, deficiency symptoms and reduced yields should occur. No visual deficiency symptoms were detected for any treatment in the experiments (all locations). All plots experienced vigorous and wellbalanced growth and development throughout the growing season. The results of these K fertility experiments supports current University of Arizona recommendations that unless exchangeable K is less than 150 ppm, crop response is not likely, although an exact critical level for exchangeable K is still lacking.

Potassium (K) fertility requirements for cotton ( Gossypium spp) have been a matter of concern due to increasing interest and emphasis on fiber quality and numerous reports of K deficiencies in various cotton producing regions. To address this matter appropriately, a thorough understanding of the chemical, physical, and mineralogical composition of the soils in question is in order. Soil samples were collected from ten sites across southern Arizona that are representative of the common agricultural soils of the region. At all locations soils were sampled to a depth of 120 cm in 30 cm increments. All soils were characterized with respect to chemical composition by the following parameters: exchangeable K, total K, cation exchange capacity and particle size analysis. With the exception of one soil (a soil not commonly employed in cotton production), none of the chemically characterized soils contained less than 150 mg K kg⁻¹ of extractable K in the surface 90 cm of soil. All of the soils contained K- bearing mica and none of the soils contained any K- fixing vermiculite. From the initial chemical and mineralogical information, K fertilization is not likely for similar situations in Arizona. Further research is under way to quantify the K-fixing ability of each soil in this survey and additional field studies are also being conducted to evaluate K fertilization in both Upland (G. hirsutum L.) and Pima (G. barbadense L.) cotton.

The computer program AZSCHED, with weather data obtained from AZMET, was used to schedule irrigations for a yield trial of Upland Cotton (DPL 90) at the Maricopa Agricultural Center. Cotton lint yields were compared between plots from eight treatments involving the combination of two irrigation efficiencies (70% and 90%), two nitrogen fertilizer placements (sidedressed and broadcast), and two phosphate fertilizer applications (0#/a and 50#/a). A potassium bromide (KBr) tracer was applied to select areas in each plot prior to the first irrigation. The total amount of fertilizer as nitrogen applied in split applications to both the sidedressed and broadcast plots was 120 #/a. The average amount of water applied to the plots were 33.5" for 70 % efficiency and 26.9" for 90% efficiency. Soil samples from each KBr applied plot were taken to a depth of 10' for analysis of bromide and nitrate to determine the depth of water movement through the soil profile. The plots were harvested on October 7, 1992. This year there was no significant difference in lint yield between any of the treatments: irrigation efficiencies, nitrogen placement, or phosphorous application.

Two field experiments were conducted in Arizona in 1992 at two locations (Maricopa and Safford). The purposes of the experiments were to validate and refine nitrogen (N) fertilization recommendations for both Upland and Pima cotton. The experiments each utilized N management tools such as pre-season soil tests for NO₃⁻-N, in-season plant tissue testing (petioles) for N fertility status, and crop monitoring to ascertain crop fruiting patterns and crop N needs. Results at both locations revealed a strong relationship between the crop fruit retention levels and N needs for the crop. This pattern was further reflected in final yield analysis as a response to the N fertilization regimes used. The effects of N fertility levels were evident in crop maturity and its relationship to lint yields.

Whitefly management has become a complex objective in Arizona in the past several years. A tremendous amount of research and extension effort is now focused on this significant pest. The purpose of this paper is to describe the position and guidelines of the University of Arizona's Cotton Team regarding the Sweetpotato Whitefly. The information presented is credited to no single source, but represents a collection of information from numerous research and extension scientists within and outside of the U of A system and careful analyses of the presently available data on whitefly management dynamics. Where possible, only the results of research are reported and suggestions based only on experience or speculation are duly noted.

Seven insecticides were evaluated in nine treatment combinations for efficacy against the sweetpotato whitefly (SPWF) and the cotton aphid (CA). Five different classes of chemistry were represented by these compounds, which were compared to an untreated check. The infestation was characterized as severe (> 300 SPWFs/sq. in.) and included a substantial number of CAs at the beginning of the evaluation ( >90 /leaf). Three applications were made in August after the onset of "stickiness." For SPWFs, three treatments compared favorably with the check, but only after three applications Orthene +Danitol, Capture alone, and Capture +Ovasyn. Intermediate control was achieved with Endosulfan +Ovasen. Rankingsfor CA control were dissimilar with Vvdate +Asana, Endosulfan +Ovasen, and Ovasen alone consistently performing better than the check. Vvdate alone, Endosulfan alone, and Orthene +Danitol were intermediate in CA control, but also significantly different from the check. Capture alone and Capture+Ovasyn which performed well for SPWF control was not efficacious against CAs. Indeed the two single pyrethroid treatments (Capture: Asana) failed to achieve any degree of CA control.

In conjunction with the 1992 cotton variety testing program (see Silvertooth 1993), 12 medium maturity varieties were evaluated for the presence of sweetpotato whitefli.es (SPWF). Three sites (Queen Creek, Maricopa, Coolidge) were selected for expression of a full range of infestation intensity. Total immatures per square inch ranged from less than 8 up to more than 8(X), depending on site, sample date and variety. The results indicated that there were significant effects of variety on SPWF numbers; however, the ranking of varieties was not always the same nor significant. Most varieties performed comparably, but one consistently had more SPWFs than the remaining varieties (chi 1 35). Comparative results from the three sites indicate that there may be separate preference and performance components which lead to the development of an infestation. Lea f hairiness was quantified front samples at one site, and the relationship of this factor to whitefly susceptibility is discussed. Two varieties, cb1135 and stv453, were found to be significantly more hairy than the remaining varieties. The results provided here represent a preliminary evaluation of the data. Further analyses will attempt to relate various crop production and agronomic factors to SPWF susceptibility (e.g., plant height, fruit retention, height:node ratio, canopy closure, growth habit, maturity, yield, crop protection regimen). One fact was clear, however. None of the varieties evaluated here demonstrated resistance to SPWFs and certainly not to the extent that a producer could eliminate substantial risk of infestation through variety selection.

In 1992, a repeat of a trap -cropping experiment was conducted for the suppression of sweetpotato whiteflies in Pima (S-6) cotton (see Ellsworth et al. 1992). The 1991 experiment showed some promise, but was characterized by low to moderate and later infestations of whiteflies than was desired. The 1992 experimental design (land area = 9.5 acres) was modified to accomplish three improvements: 1) the cotton crop area was doubled in size to 8 rows by 50 ft to improve the ratio of crop to trap area, 2) a fourth treatment was added to form a Latin square design which consisted of cotton plots surrounded only by bareground (i.e., no trap crop): the other three were surrounded by Wright groundcherry that was untreated or treated with 1X or 2X rates of soil-applied aldicarb, and 3) melons (1 row X667') were late planted between blocks to ensure locally abundant whiteflies during the time of the test. The melons were watered regularly in order to retain whiteflies until the start of the test. Early groundcherry establishment was variable and later compromised by insufficient water. This prompted later than usual flushes of groundcherry growth and delayed canopy development. This fact coupled by the intense level of whitefly movement following melon dry -down effectively overwhelmed the insufficiently developed trap crop. Aldicarb was applied on two dates (7/29 & 8/15), and whiteflies were sampled from all plots five times through August. The sampling data are preliminary at this point, but several observations were apparent: 1) the groundcherry trap crop was insufficiently developed to protect the Pima crop, 2) the addition of melons to the system dramatically increased the ,cumbers of locally abundant whiteflies, 3) maintaining the melons in good condition (i.e., well- watered) effectively retained whiteflies in the melons until dry-down, 4) upon dry-down, the melons released overwhelming numbers of adult whiteflies which could not be suppressed on the groundcherry trap crop before reaching the adjacent cotton, 5) the groundcherry was still selectively attractive to the whiteflies (relative to cotton), but was insufficiently developed w trap and retain the huge numbers of dispersing whiteflies, 6) soil - applied aldicarb did accomplish some degree of control of whiteflies on the groundcherry plants, but was inadequate in the face of the tremendous immigration of whitefly adults, 7) the intense whitefly pressure ultimately killed the majority of immature groundcheny plants with the aldicarb-treated plants lasting somewhat longer than the untreated plants, and 8) the yield and quality of the adjacent, late -planted Pima crop was commercially unacceptable and judged to be virtually a total loss. The failure of this implementation of the trap -cropping concept does not preclude the possibility that a better implementation would have succeeded; however, the observation that melons in close proximity to the test area dramatically changed the number of locally dispersing adult whiteflies cannot be denied. It would seem unlikely that a suitable trap crop system could be developed where such an intense proximate source and near instantaneous release of thousands of whiteflies (i.e., at dry-down of melons) is occurring.

Trap crops were employed against the pink bollworm (PBW) as a part of a community-wide IPM program in Pima County, AZ. Levels of PBW larvae in the early squares of the trap crops were extraordinarily high, indicating that the trap crops were drawing overwintered PBW moths in from wide areas. This concentrated the overwintered moths in small areas where they could be easily and economically destroyed.

Insect damage impacts tremendously on the value of the Arizona cotton crop. As traditional pesticides become increasingly less useful, due to insect resistance and regulatory problems, new methods for insect control are needed. For these reasons, we engineered genes encoding protease inhibitors (PIs) from Manduca sexta (tobacco hornworm), for expression in cotton, with the hope that these inhibitors would have insecticidal activity. Transgenic plants containing PIs have been generated: 22 fertile lines of the duplicated 35S promoter anti-elastase, 4 fertile lines of the anti -chymotrypsin and 5 fertile lines of the anti -trypsin. Over 3,000 T-1 seeds have been collected and T-2 generation seeds are in production. Many crosses have been made into Delta Pine 16, 90 and 5415 respectively. No significant effect of the PIs on boll number or seed yield was observed. Insect tests have been conducted and the results indicate that plants expressing the protease inhibitors (PI's) have decreased emergence of whiteflies compared to control plants. We believe this research is a significant step towards a bio- pesticide producing Arizona cotton variety.

Surveys of whitefly parasites in cotton showed few or none were present during July and October in some areas, preliminary observations of sticky traps show that large numbers of parasites were present in some fields during October.

RAPD -PCR was used to detect differences at the DNA level between the A and B forms of B. tabaci. All twenty of the RAPD primers tested distinguished readily between the forms. These primers also distinguished between the forms at the egg and nymph stage. Genetic similarity statistics indicate that these two forms of B. tabaci were no more closely related to each other than to bayberry whitefly (Parabemisia mvricae) or bandedwinged whitefly (Trialeurodes abutilonea). DNA from B. tabaci collected from 11 locations around the world was also analyzed. These insects could be classified into six distinct groups, suggesting there are more than two variant forms of B. tabaci. A comprehensive examination of all variant types of B. tabaci will have to be conducted before a concise definition of the taxonomic relationship between the 'A' and 'B' forms can be determined.

Surveys for adult sweetpotato whitefly parasites on ornamentals in urban areas and in cultivated cotton fields show high parasite activity in urban areas vs. activity in cultivated cotton fields. A previously unreported Drapetis spp. fly was identified and found to occur in cotton fields in several areas in the state.

Deltapine 50 (DP -50) and Stoneville 506 (ST -506), short season cultivars of upland cotton, Gossvpium hirsutum L., were grown under weekly or biweekly irrigation schedules in 0.2 ha plots in a split plot design at Maricopa, AZ. The seasonal average numbers of sweetpotato whitefly eggs and nymphs were 24% greater on leaves of plants irrigated biweekly. The leaves of ST-506 had 26% greater numbers of eggs and nymphs than did leaves of DP -50. Samples of lint from the two cultivars irrigated biweekly had 32 % more sugar than did lint from the cultivars irrigated weekly (weekly = 0.28 ± 0.02% , biweekly = 0.41% ± 0.03% sugar). Our results indicate that the numbers of immature sweetpotato whitefly on cotton plants can be reduced by 47% by selecting a less susceptible cultivar and avoiding plant water stress.

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